1. Field of the Invention
The present general inventive concept relates to a print control terminal, an image forming apparatus, a print control method, and an image forming method, and more particularly, to a print control terminal, an image forming apparatus, a print control method, and an image forming method to improve the quality of an output image in a manner of changing a transparency multiple number according to the characteristics of a halftone screen.
2. Description of the Related Art
Usually, an image forming apparatus indicates a device which prints print data generated by a terminal such as a computer on a printing medium. Such an image forming apparatus may be a copy machine, a printer, a fax machine, or an MFP (multifunction peripheral) which integrates functions of these devices in one device.
To output an image containing a plurality of objects, an image forming apparatus processes the objects starting from the ones in the rearmost portion to the ones in the foremost portion, stores the processed objects in an output buffer, and then outputs the image. If there is an object having transparency, the image forming apparatus embodies the transparency using masking. That is, the image forming apparatus assigns a mask value of 0 or 1 to each pixel. If mask value 0 is assigned to a pixel, the image forming apparatus replaces the value pre-stored in the output buffer with color of the object having transparency, and if mask value 1 is assigned to a pixel, the image forming apparatus retains the value pre-stored in the output buffer.
There are generally two methods to process transparency: a download pattern method, and a bitmap transparency method. The download pattern method tilts a specific pattern (for example, a pattern having 16×16 pixels) to fit in a predetermined area, creates a mask, and processes a transparency using the mask, which is used when a large area should be processed to have a constant transparency. The bitmap transparency method assigns a mask value one by one for each pixel, which is used for objects having a gradation transparency where each pixel has a different transparency value.
In the download pattern method, a specific pattern (for example, a pattern having 16×16 pixels) may be either tilted as it is, or be enlarged and then tilted. Specifically, FIGS. 3A and 3B illustrate an image in which a download pattern having transparency of 50% (FIG. 3A) is enlarged to twice the width and the height (FIG. 3B). The ratio of enlarging a pattern is referred to as a transparency multiple number, and the transparency multiple number will be described as (width times)×(height times), hereinbelow. For instance, transparency multiple number 4×4 represents that a download pattern having transparency of 50% is enlarged to four times the width and the height.
Conventional image forming apparatuses process a transparency for all of the output options and all colors using only a single transparency pattern. However, if a specific halftone screen is combined with a specific transparency multiple number, the transparency multiple number needs to be adjusted according to the halftone screen to prevent image quality degradation.
FIGS. 4A and 4B are examples of output images to which the same transparency multiple number 4×4 and different halftone screens are applied. Specifically, FIG. 4A illustrates an image to which a halftone screen having 190 line per inches (LPI) and transparency multiple number 4×4 are applied, and FIG. 4B illustrates an image to which a halftone screen having C:158 LPI, M:172 LPI, and transparency multiple number 4×4 are applied.
Referring to FIGS. 4A and 4B, it can be seen that even when the same transparency multiple number is used to process the transparency of an image, image quality degradation such as visible white lines may occur when a specific halftone screen is applied.